Earth’s climate system – a complex framework
1.1 > Different components of the climate system react to perturbations at different rates. The deep ocean, for example, is an important cause of the slow response of climate. The coloured area on the top scale represents the short time span of a human life.
The inertia of climate
As we all learned in school, the world’s oceans are one of the most important elements in the global climate system. But what does “climate” actually mean? The difference between weather and climate can be expressed in a single sentence: “Climate is what you expect; weather is what you get.” This reveals a fundamental difference between weather and climate. Weather research is concerned with the formation, movement, and prediction of the individual elements of weather, such as a particular low-pressure system or a hurricane. Climate research, on the other hand, deals with the more comprehensive totality of low pressure systems and hurricanes, and is dedicated to addressing questions such as how many midlatitudinal storms or hurricanes will occur next year, or whether they will become more frequent or intense in the coming years as a result of global warming. So the term “weather” refers to short-term events in the atmosphere, while “climate” relates to longer time periods. For describing climate, as a rule, a time span of 30 years is generally used as a frame of reference.
- People mainly perceive climate change as changes in atmospheric variables, for example, variations in temperature or precipitation. In principle, due to its chaotic dynamics, the atmosphere itself can generate many natural climatic changes. One example of this is the North Atlantic oscillation (NAO), which significantly influences the climate over parts of Europe and North America. It is a kind of pressure fluctuation between the Icelandic Low and the Azores High that determines the strength of winter westerly winds across the North Atlantic. If these are strong, the result is mild and rainy weather in Western Europe; if they are weak it is dry and cold. These kinds of natural oscillations make it difficult to recognize anthropogenic climate changes due to an enhanced greenhouse effect.
The atmosphere is not an isolated system. It interacts with other components of the Earth system – the oceans, for example. But it is also in contact with the cryosphere (ice and snow), the biosphere (animals and plants), the pedosphere (soil) and the lithosphere (rocks). All of these elements together compose the climate system, whose individual components and processes are connected and influence each other in diverse ways.
- The atmosphere is not an isolated system. It interacts with other components of the Earth system – the oceans, for example. But it is also in contact with the cryosphere (ice and snow), the biosphere (animals and plants), the pedosphere (soil) and the lithosphere (rocks). All of these elements together compose the climate system, whose individual components and processes are connected and influence each other in diverse ways.
- These components all react to change at different rates. The atmosphere adjusts to the conditions at the Earth’s surface such as ocean temperature or ice cover within a few hours to days. Furthermore, weather is variable and can only be predicted a few days in advance. In fact, it has been shown that the theoretical limit of weather predictability is around 14 days. Currents in the deep sea, however, require several centuries to react fully to changing boundary conditions such as variations in the North Atlantic oscillation, which cause changes in temperature and precipitation at the sea surface and thus drive motion at greater depths. A large continental ice mass such as the Antarctic ice sheet, as a result of climate change, presumably undergoes change over many millennia, and without counteractive measures it will gradually melt on this time scale. The predictability of climate is based on the interactions between the atmosphere and the more inert climate subsystems, particularly the oceans. Within this scheme, the various components of the climate system move at completely different rates. Low-pressure systems can drift hundreds of kilometres within days. Ocean currents, on the other hand, often creep along at a few metres per minute. In addition, the individual components possess different thermal conductivities and heat capacities. Water, for instance, stores large amounts of solar heat for long periods of time.
Climate changes can be triggered in two different ways – by internal and external forces. The internal forces include:
- Changes in a single climate component, for example, an anomalous ocean current;
- Changes in the interactions between different climate components, for example, between the ocean and atmosphere.
Compared to these, the external mechanisms at first glance appear to have nothing to do with the climate system. These include:
- The very slow drift of continents, which moves land masses into different climate zones over millions of years;
- The changing intensity of radiation emitted by the sun. The radiation energy of the sun fluctuates over time and changes temperatures on Earth;
- Volcanic eruptions, which inject ash and sulphur compounds into the atmosphere, influence the Earth’s radiation budget and thus affect climate. >